Or how slow exactly "slow" is in seconds :-p ... but really it shouldn't be that hard for Canon to reproduce if they set their mind on it ... or they already have and discovered they won't be able to fix it? Anyway, I hope the matter gets cleared up before I finally decide if to get the 6d or 5d3 :-o

Just coming back to this thread...lets not get off about how to properly expose a file...it is really off topic.....Ican tell you in a specific case....I took a candid of two women...one caucasian and on very dark afroamerican...thecaucasian was properly exposed....the other way under....bringing here back up left an incredible amount of noise...this was with flash at iso 400. I also know that there are noise problems at lower isos even with proper exposure.

Anyhow....the focusing problem with AF assist occurs at almost any ev....I haven't verified this in brightsunlight yet....but I was shooting headshots at a local hospital yesterday in bright interior lighting....now I usemy 600 rt's in group mode with 4 lights total....the commander light being on the camera. I have shut off the flash from the commander...but kept the af light....thing would hunt to focus on person's face using one of thecross sensors in the vertical quadrant (upper right in viewfinder). When I shut of the af assist...it was definitelyfaster, but not as fast as my Mark2, which I had with me to compare.

Just coming back to this thread...lets not get off about how to properly expose a file...it is really off topic.....Ican tell you in a specific case....I took a candid of two women...one caucasian and on very dark afroamerican...thecaucasian was properly exposed....the other way under....bringing here back up left an incredible amount of noise...this was with flash at iso 400. I also know that there are noise problems at lower isos even with proper exposure.

Anyhow....the focusing problem with AF assist occurs at almost any ev....I haven't verified this in brightsunlight yet....but I was shooting headshots at a local hospital yesterday in bright interior lighting....now I usemy 600 rt's in group mode with 4 lights total....the commander light being on the camera. I have shut off the flash from the commander...but kept the af light....thing would hunt to focus on person's face using one of thecross sensors in the vertical quadrant (upper right in viewfinder). When I shut of the af assist...it was definitelyfaster, but not as fast as my Mark2, which I had with me to compare.

Sounds like what I was dealing with. I couldn't get focus lock in regular indoor room light for several seconds. It was a joke... on me. After I returned the camera for dealer exchange for a new replacement (not a refurb), the AF problem seems to be gone. I was really worried that Canon had somehow totally screwed up the AF design but I guess there are just a lot of cameras out there with this AF problem that likely isn't a design problem, it's a QA problem on the assembly line(?). I guess.

As time moves forward, there seem to be TWO SIDES...- Those that DON'T HAVE AF PROBLEMS and- Those that DO HAVE AF PROBLEMS.

I feel like I thankfully moved from the DO to the DON'T side. Don't waste time trying to fix it yourself or work around it. See what Canon will do for you and let us know how it goes!!

I appreciate your thanks dlleno. No offense but honestly, this is really bad to know.

I wish this thread didn't even exist and I had all the hours back in my life that I spent trying to figure this out and dealing with it. I'm sure the others feel the same way. It is a relief that it came to a positive end though. Thanks to this forum, I was able to return it for exchange instead of having to wait and wait dealing with a warranty repair. If I (we) can help someone else come to the same conclusion, that's good.

I'm tracking you -- this is bad for the aparent QC during manufacturing, but outstanding information re: how to resolve this. I suspect the story is not ended yet though - Canon technical support told me that the AF assist beam is not supported with this combination (5D3 and 600ex), and one wonders why that would be and what unofficial or official result will come about. Maybe they fixed it silently without acknowledging the issue.

So, to bring clarity: you're saying your 5D3 uses the AF assist beam just fine with half-pressed shutter, or that it focuses great in low light when you press the shutter all the way down.

now then, bring me up to speed or refer me to a previous post I've overlooked: What was it about this forum that enabled the "return" versus repair option?

dlleno - Go back in this thread to page 9 and you'll see the update I posted about how the replacement 5D3 AF seems to be working for me now. Look back further and you'll see several posts by me and others discussing the problem before that.

Marsu42 - my guess is that perhaps dlleno spoke with a misinformed tech rep. Who knows? I find that statement hard to believe as well. For that matter, how can any fairly recent/decent Canon brand flash be 'not supported' on a Canon camera? If new Canon flash units (worth $600 each) aren't supported on Canon cameras (worth $3500), then I guess I'll just go buy cheap Chinese knockoffs that likely work better anyway!! Dammit. So there!

I said I would compare my 5d3 with 430exii VS 1dx with same 430exii in very low light....

Bottom line, the 430exii didn't work on the 5d3. In a very dark basement, it couldn't/wouldn't acquire focus...several OOF shots later I put the 1dx on with the same flash. It worked like a charm, not a single problem....took maybe 1/2 sec to acquire focus in the exact same dark basement.....used the 24-105 for both.

One thing I noticed is that the AF beam didn't even work on the 5d3. I have noticed this "random" issue in the past where the beam works/or doesn't work for no apparent reason with the 5d3.

So I wonder what it actual problem is?? Is it firmware, hardware or those drunk assembly line workers again, turning capacitor #651-A (and sometimes B!) around on every 5th AF board just to screw with us?

Shot with both my mark2 and mark3 at an event yesterday....the mark 3 actually caused me to miss shots..when I switched to the mk2...all was well....this is in a fairly dark venue using multiple 600 rts and focusassist. I tried various settings with the mark3...one shot with and w/o af assist, ai servo using multiple points,my conclusion is I can't count on the mk 3 for important stuff just yet.

Here's an interesting post on this forum...he comes to the same conclusion I did....the mk3 focus seems to bea 2 step process.

perhaps the n-step retry/credence process that accomplishes the extraordinary AF consistency, repeatability and accuracy of the 5D3 (producing very low std deviations in Roger's tests) is also what consumes the additional time in low light. sounds like a firmware issue to me; If the feedback loop cannot be tuned for greater speed in low light, then provide a CF or AF configruation giving user the choice to reliquish some of that extraordinary repeatability in low light to acheive greater AF speed. Hard to imagine that the 6D aparent superiority in this regard is intentional.

I have not had a chance to follow-up on the T1i and 5D3 comparisons from a while back, but ...I did shot again this weekend with 5D3 and 600EX at night and it was an exercise in frustration to say the least. Here is what I observed:

1. As noted by someone else previously, distance plays a big roll in the AF Assist beam effectiveness. I was shooting outside in a town square, very low light, 100mm L, trying to get my wife and son shoulder up with a bit a of Xmas tree lights in the background. At the distance necessary to make that framing possible the focus assist was virtually useless, not locking at all or shooting completely OOF shots. This was not remedied by the suggestion of not waiting for focus confirm and just pressing the shutter release button all the way (it would get me OOF shots when it would actually fire). Turning the flash off resulted in a focused pictures (not instantly, but acceptable given the low light). I did not have my T1i handy to compare but I did not have this problem shooting the same shots in the same square, at the same time of night, with the 430EX II and the T1i. (Not scientific, I know but there it is...)

2. At closer distances, the focus assist worked but slowly. I would get the shots in focus but I missed the moment because of the hesitation. This was maddening to say the least. Here I am with $5K worth of camera kit and I could not get a decent shot that would have been possible with a lot less.

I continue to be disheartened and hope that the issue is identified, a fix is possible, and that it will be release within the next few months. I'm kind of gutted right now.

I think there is some credence to your argument. I just hope that if they do the firmware, we do not lose accuracy to any great degree. The mark 2 is pretty well 99% accuracy when using the center spot with afassist...so this should be doable with the new camera. I am so confident at receptions with the old camera thatI frequent just point the camera at a group of people I want to capture without even looking thru the viewfinder.